Pliocene white pine (Pinus subgenus Strobus) needles from western Yunnan, southwestern China

Abstract

The fossil records of Pinus L. are abundant since the Late Cretaceous, especially for the subgenus Pinus L. (the hard pines). However, those of the subgenus Strobus (D. Don) Lemmon (the white or soft pines) are not well documented. In this study, we describe a new species of white pines, Pinus plioarmandii sp. nov., from the Pliocene of western Yunnan, southwestern China. This species mostly resembles extant P. armandii Franch. in gross morphology and cuticular structure of needles. Molecular dating showed that the Asian white pines split into two lineages around the Late Miocene, and the Pinus armandii clade diverged at the Early Pliocene. The present fossil occurrence indicates that Pinus armandii might originate in southwest China and probably in the western Yunnan. The glacial events during the Pleistocene might be the major factors for the retreat of the white pines from western Yunnan, and the rapid uplift of the Yunnan Plateau and deep incision of the river valleys since the Pliocene had posed a significant geographic barrier for their reconnection in the subsequent warm climate condition.